The technique of introducing information at one end of a gas discharge display device as a pattern of on or off states at discrete discharge sites and shifting such information to a selected display position within the device is known in the art. In one known system, information is entered to a first vertical electrode and a system of multiphased voltages is applied to succeeding sets of vertical electrodes of the display device to shift data laterally therein. In such case there is only one information light spot on at a time. Other systems use auxiliary intermediate electrodes (reference Andoh et al U.S. Pat. No. 3,801,851), the voltage amplitude and polarity being selected to vary the size of the discharge spot for shifting purposes. Other data shift systems depend on different dielectric thicknesses or dielectric constants of two opposed dielectric layers (reference Andoh et al U.S. Pat. NO. 3,803,440). In still another prior display data shifting system, the wall voltage produced at one site is used to initiate a discharge, having a longer path length, between one site and a next adjacent site (reference McDowell et al U.S. Pat. No. 3,795,908). The longer path length reduces the operating margins and requires use of the wall charge mechanism to effect lateral transfer of information. Finally, in still another prior art system, tapered and similarly shaped electrodes are used for assuring an overlap of the wall charge of one site with an adjacent one for transfer purposes (reference German Offenlegungsschrift No. 2,130,706). Other shift register devices and techniques are disclosed by U.S. Pat. Nos. 3,775,764 (Gaur) and 3,789,264 (Janning).
In accordance with the practice of this invention, the principle of discharge logic is combined with a multiphase data shift to provide improved display system in a multiple gas discharge display/memory device.
Multiple gas discharge display and/or memory panels of the type with which the present invention is concerned are characterized by an ionizable gaseous medium, usually a mixture of at least two gases at an appropriate gas pressure, in a thin gas chamber or space between a pair of opposed dielectric charge storage members which are backed by conductor (electrode) members, the conductor members backing each dielectric member typically being appropriately oriented so as to define a plurality of discrete gas discharge units or cells.
In some prior art panels the discharge cells are additionally defined by surrounding or confining physical structure such as apertures in perforated glass plates and the like so as to be physically isolated relative to other cells. In either case, with or without the confining physical structure, charges (electrons, ions) produced upon ionization of the elemental gas volume of a selected discharge cell, when proper alternating operating potentials are applied to selected conductors thereof, are collected upon the surfaces of the dielectric at specifically defined locations and constitute an electrical field opposing the electrical field which created them so as to terminate the discharge for the remainder of the half cycle and aid in the initiation of a discharge on a succeeding opposite half cycle of applied voltage, such charges as are stored constituting an electrical memory.
Thus, the dielectric layers prevent the passage of substantial conductive current from the conductor members to the gaseous medium and also serve as collecting surfaces for ionized gaseous medium charges (electrons, ions) during the alternate half cycles of the A.C. operating potentials, such charges collecting first on one elemental or discrete dielectric surface area and then on an opposing elemental or discrete dielectric surface area on alternate half cycles to constitute an electrical memory.
An example of a panel structure containing non-physically-isolated or open discharge cells is disclosed in U.S. Pat. No. 3,499,167 issued to Theodore C. Baker, et al.
An example of a panel containing physically isolated cells is disclosed in the article by D. L. Bitzer and H. G. Slottow entitled "The Plasma Display Panel--A Digitally Addressable Display With Inherent Memory", Proceeding of the Fall Joint Computer Conference, IEEE, San Francisco, California, Nov. 1966, pp. 541-547. Also reference is made to U.S. Pat. No. 3,559,190.
In the construction of the panel, a continuous volume of ionizable gas is confined between a pair of dielectric surfaces backed by conductor arrays typically forming matrix elements. The cross conductor arrays may be orthogonally related (but any other configuration of conductor arrays may be used) to define a plurality of opposed pairs of charge storage areas on the surfaces of the dielectric bounding or confining the gas. Thus, for a conductor matrix having H rows and C columns the number of elemental discharge cells will be the product H .times. C and the number of elemental or discrete areas will be twice the number of such elemental discharge cells.
In addition, the panel may comprise a so-called monolithic structure in which the conductor arrays are created on a single substrate and wherein two or more arrays are separated from each other and from the gaseous medium by at least one insulating member. In such a device the gas discharge takes place not between two opposing electrodes, but between two contiguous or adjacent electrodes on the same substrate; the gas being confined between the substrate and an outer retaining wall. Reference is made to U.S. Pat. No. 3,787,106 issued to Schermerhorn.
It is also feasible to have a gas discharge device wherein some of the conductive or electrode members are in direct contact with the gaseous medium and the remaining electrode members are appropriately insulated from such gas, i.e., at least one insulated electrode.
In addition to the matrix configuration, the conductor arrays may be shaped otherwise. Accordingly, while the preferred conductor arrangement is of the crossed grid type as discussed herein, it is likewise apparent that where a maximal variety of two dimensional display patterns is not necessary, as where specific standardized visual shapes (e.g., numerals, letters, words, etc.) are to be formed and image resolution is not critical, the conductors may be shaped accordingly, i.e., a segmented display.
The gas is one which produces visible light or invisible radiation which stimulates a phosphor (if visual display is an objective) and a copious supply of charges (ions and electrons) during discharge.
In prior art, a wide variety of gases and gas mixtures have been utilized as the gaseous medium in a gas discharge device. Typical of such gases include CO; CO.sub.2 ; halogens; nitrogen; NH.sub.3 ; oxygen; water vapor; hydrogen; hydrocarbons; P.sub.2 O.sub.5 ; boron fluoride, acid fumes; TiCl.sub.4 ; air; H.sub.2 O.sub.2 ; vapors of sodium, mercury, thallium, cadmium, rubidium, and cesium; carbon disulfide, H.sub.2 S; deoxygenated air; phosphorus vapors; C.sub.2 H.sub.2 ; CH.sub.4 ; naphthalene vapor; anthracene; freon; ethyl alcohol; methylene bromide; heavy hydrogen; sulfur hexafluoride, tritium; radioactive gases; and the rare or inert gases.
In one embodiment, the medium comprises at least one rare gas, more preferably at least two, selected from helium, neon, argon, krypton, or xenon.
In an open cell Baker, et al. type panel, the gas pressure and the electric field are sufficient to laterally confine charges generated on discharge within elemental or discrete dielectric areas within the perimeter of such areas, especially in a panel containing non-isolated discharge cells. As described in the Baker, et al. patent, the space between the dielectric surfaces occupied by the gas is such as to permit photons generated on discharge in a selected discrete or elemental volume of gas to pass freely through the gas space and strike surface areas of dielectric remote from the selected discrete volumes, such remote, photon struck dielectric surface areas thereby emitting electrons so as to condition at least one elemental volume other than the elemental volume in which the photons originated.
With respect to the memory function of a given discharge panel, the allowable distance or spacing between the dielectric surfaces depends, inter alia, on the frequency of the alternating current supply, the distance typically being greater for lower frequencies.
While the prior art does disclose gaseous discharge devices having externally positioned electrodes for initiating a gaseous discharge, sometimes called "electrodeless discharge", such prior art devices utilized frequencies and spacing or discharge volumes and operating pressures such that although discharges are initiated in the gaseous medium, such discharges are ineffective or not utilized for charge generation and storage at higher frequencies; although charge storage may be realized at lower frequencies, such charge storage has not been utilized in a display/memory device in the manner of the Bitzer-Slottow or Baker, et al. invention.
The term "memory margin" is defined herein as ##EQU1## where V.sub.f is the half amplitude of the smallest sustaining voltage signal which results in a discharge every half cycle, but at which the cell is not bi-stable and V.sub.E is the half amplitude of the minimum applied voltage sufficient to sustain discharges once initiated.
It will be understood that the basic electrical phenomenon utilized in this invention is the generation of charges (ions and electrons) alternately storable at pairs of opposed or facing discrete points or areas on a pair of dielectric surfaces backed by conductors connected to a source of operating potential. Such stored charges result in an electrical field opposing the field produced by the applied potential that created them and hence operate to terminate ionization in the elemental gas volume between opposed or facing discrete points or areas of dielectric surface. The term "sustain a discharge" means producing a sequence of momentary discharges, at least one discharge for each half cycle of applied alternating sustaining voltage, once the elemental gas volume has been fired, to maintain alternate storing of charges at pairs of opposed discrete areas on the dielectric surfaces.
As used herein, a cell is in the "on state" when a quantity of charge is stored in the cell such that on each half cycle of the sustaining voltage, a gaseous discharge is produced. In addition to the sustaining voltage, other voltages may be utilized to operate the panel.
In the operation of a multiple gaseous discharge device, of the type described hereinbefore, it is necessary to condition the discrete elemental gas volume of each discharge cell by supplying at least one free electron thereto such that a gaseous discharge can be initiated when the cell is addressed with an appropriate voltage signal. The prior art has disclosed and practiced various means for conditioning gaseous discharge cells.
One external conditioning method comprises the use of external radiation, such as flooding part or all of the gaseous medium of the panel with ultraviolet radiation. This external conditioning method has the obvious disadvantage that it is not always convenient or possible to provide external radiation to a panel, especially if the panel is in a remote position. Likewise, an external UV source required auxiliary equipment. Accordingly, the use of internal conditioning is generally preferred.
One internal conditioning means comprises using internal radiation, such as by the inclusion of a radioactive material.
For the fabrication, structure, and operation of a multiple gas discharge display/memory device, reference is made to U.S. Pat. Nos. 3,499,167 issued to Baker et al; 3,559,190 issued to Bitzer et al; 3,603,836 issued to Grier; 3,631,287 issued to Hoehn; 3,634,719 issued to Ernsthausen; 3,787,106 issued to Schermerhorn; 3,806,761 issued to Bode et al; 3,701,184 issued to Grier; 3,746,420 issued to Baker et al; 3,823,393 issued to Byrum et al; 3,762,901 issued to Salisbury et al; and 3,749,959 issued to Schmersal et al; all of which patents are hereby incorporated by reference.